When the field winding is connected in series with the armature winding while supplying the load then the generator is called series generator. It is shown in the Fig. 1.

Field winding, in this case is denoted as S1 and S2. The resistance of series field winding is very small and hence naturally it has less number of turns of thick cross-section wire as shown in the Fig. 1.

Fig. 1 Series generators

Let Rse be the resistance of the series field winding.

1.1 Voltage and current Relations

As all armature, field and load are in series they carry the same current.

... Ia = Ise = IL

Where Ise = Current through series field winding.

Now in addition to drop Ia Ra, induced e.m.f. has to supply voltage drop across series field winding too. This isIse Rse i.e. Ia Rse as Ia = Ise. So voltage equations can be written as,